Thermionic valve



May 15, 1934. H. J. ROUND THERMIONIC VALVE Filed June 21, 1928 INVENTOR it JOSEPH ROUND BY AT RNEY Patented May 15, 1934 UNITED STATES THERMIONIC VALVE Henry Joseph Round, London,

to Radio Corporation of America,

of Delaware England, assignor a corporation Application June 21, 1928, Serial No. 287,144 In Great Britain July 27, 1927 4 Claims.

This invention relates to thermionic valves, and more particularly to thermionic valves of the kind comprising an anode, a cathode, a control grid and a so-called screening grid, interposed between the anode and the control grid. Such a thermionic valve is described in my United States Patent No. 1,894,599, January 1'7, 1933.

It is found in practice that the anode currentanode voltage characteristic of a valve of the kind referred to tends to fall away, giving a falling current characteristic, when the voltage applied to the anode is less than that applied to the screening grid. Such a falling characteristicwhich is frequently undesirableis believed to be due to secondary emission of electrons from the anode, which electrons tend to fall back on the outer grid.

According to this invention there is provided in a valve of the kind referred to an additional grid-like electrode, situated between the screening grid and the anode and connected to a point of substantially zero potential, such as the oathode, so as to have a tendency to prevent electrons falling back upon the said screening grid.

The invention is illustrated in the accompanying drawing.

Referring to the drawing, a thermionic valve comprises an envelope 1 enclosing a cathode 2, an anode 3, a control grid 4 and a so-called screening grid 5, all as described in my United States Patent 1,894,599. Located between the screening grid and the anode is an additional grid-like electrode 6 of more open mesh than the screening grid, the said electrode being connected in practice to a point at or near zero potential-for example, to the cathode or to earth.

The provision of the additional grid-like electrode renders necessary the use of a somewhat higher anode potential, owing to the shielding eiiect the said additional grid introduces, and at the same time it reduces the tendency of the screening grid to pull back the emitted secondary electrons.

Thus the increase of anode potential and the decrease of effective potential of the screening grid exhibited at the anode surface, together prevent the emitted secondary electrons falling anywhere except back on the anode.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:-

1. An electron discharge device comprising a sealed highly evacuated tubular envelope enclosing a thermionic electron emitting cathode, a disc anode mounted in a plane perpendicular to the longitudinal axis of said envelope, a control grid adjacent said cathode, a screen grid between said control grid and said anode, and

an additional grid of more open mesh than said screen grid between said screen grid and said anode, said grids being mounted to extend transversely of said envelope in planes parallel to the plane of said anode and perpendicular to the longitudinal axis of said envelope and to be passed successively by the electron stream from said cathode to said anode.

2. An electron discharge device comprising a sealed highly evacuated tubular envelope enclosing a thermionic electron emitting cathode, a disc anode mounted in a plane perpendicular to the longitudinal axis of said envelope, a control grid adjacent said cathode, a screen grid between said control grid and said anode, and an additional grid between said screen grid and said anode, said grids being mounted to extend transversely of said envelope in planes parallel to the plane of said anode and perpendicular to the longitudinal axis of said envelope and to be passed successively by the electron stream from said cathode to said anode, and an electrical connection between said additional grid and said cathode to maintain said additional grid at substantially the potential of said cathode.

3. 'An electron discharge device comprising a sealed highly evacuated tubular envelope enclosing a filamentary electron-emitting cathode mounted in a plane perpendicular to the longitudinal axis of said envelope, a control grid surrounding said cathode and extending in planes parallel thereto, a screen grid extending transversely of said envelope parallel to the plane of said cathode, means for supporting said cathode and said grids from one end of said envelope, a disc anode mounted transversely of said envelope near the other end of said envelope, a transverse auxiliary grid electrode between said anode and said screen grid, and means for supporting said anode and said auxiliary grid from the other end of said envelope.

4. An electron discharge device comprising a sealed highly evacuated tubular envelope enclosing a filamentary electron-emitting cathode mounted in a plane perpendicular to the longitudinal axis of said envelope, a control grid surrounding said cathode and extending in planes parallel thereto, a screen grid extending transversely of said envelope parallel to the plane of said cathode, means for supporting said cathode and said grids from one end of said envelope, a disc anode mounted transversely of said envelope near the other end of said envelope, a transverse auxiliary grid electrode between said anode and said screen grid electrically connected directly to the cathode, and means for supporting said anode and said auxiliary grid from the other end of said envelope.

HENRY JOSEPH ROUND. 

